The present invention relates to preparation of lenses for vision improvement and, more specifically, to a novel and useful new improvement in the preparation of a lens circumference for secure fitting a pre-existing frame.
In the vision assistance industry, it is a very common situation to be presented with an existing pair of eyeglasses of known optical characteristics wherein one of the lenses has been destroyed, although the frame remains intact. For reasons of economy, replacement of a single broken lens is increasingly preferred over the alternative of manufacturing a complete substitute set of eyeglasses. This is partly due to the development of the market for designer frames. As in other fashion-driven markets, designer frames purchased at any given time may be obsolete and no longer available from the manufacturer only months later. Thus obtaining a desired but obsolete designer frame often becomes a major factor of both cost and delay in providing the customer with vision assistance. For all of these reasons, it is often preferred to utilize the existing frame and fit a new lens to that frame.
However, a further difficulty has arisen, also as a result of the market for designer frames. There is no longer a standard outline or circumference for lenses used in eyeglasses. Not only the lens size but the circumference has seen variation over a broad range of patterns. Some lenses are approximately circular in shape, whereas other lenses are approximately rectangular in character while others are approximately triangular or some combination of these attributes.
One method of conforming lenses to frame sockets is currently widely used in the retail vision assistance field. In this method, a damaged lens is removed from the frame, and the circumference of the open socket is duplicated by tracing the inside thereof with a pencil or the like onto a flat cuttable blank. This blank is typcially made of light-weight stiff plastic which permits cutting so that the blank is ultimately contoured to fit in the empty socket. The blank thus contoured is then mounted to serve as the master pattern in an edging machine such as those which are commercially available from Weco or AIT. In the edging machine, both the contoured pattern and a replacement lens are mounted on a floating axle which is turned by a motor. As the axle turns, the circumference of the contoured pattern is rotated in proximity with a pattern follower wheel while the lens is rotated in contact with a grinding surface. The grinding surface selectively reduces the radius of each segment of the lens periphery, relative to its center, until the radius of a segment equals that of the corresponding portion of the contoured pattern. The contoured pattern thereafter acts as a cam and maintains the floating axle at a height above the grinding surface so that no further grinding takes place on that portion of the circumference. The process is completed when the portion at the shortest radius from the lens center is completely ground. The lens is then removed and placed in the frame socket.
If it is desired to produce two lenses for an eyeglass frame, either the contoured pattern or the second new lens may be reversed on the floating axle so as to take advantage of mirror-image symmetry of eyeglass frame sockets relative to one another. The grinding process then continues in the same fashion until the edge of the second new lens is completely contoured to fit the remaining frame socket.
There are several detrimental aspects of this procedure which contribute to its costliness and increase the time required for successful completion. First, the pattern blank must be accurately cut and contoured to fit the open socket of the frame. This is not easily achieved by the present method of tracing through the socket onto the pattern. Since tracing is a manual step, such factors as pen angle variance and motion of the blank or frame can adversely effect the accuracy of the resulting trace. Therefore, it is typical for the practitioner to make an initial cut outside the trace and then reiterate a process of trimming the pattern and testing its fit in the socket. Errors which reduce any portion of the pattern contour below the size needed for snug fit in the socket require recommencement of the process.
Another difficulty is related to the manner in which the contoured pattern is related to the new lens to be contoured. All such new lenses are optically ground prior to edge grinding. After optical preparation, each lens must be carefully centered on the floating axle of the edge grinder. A common off-the-shelf device known as a lensometer is utilized to locate and mark the optical center of each lens. The lens is then mounted to the floating axle in a well-known manner. The contoured pattern is flat and exhibits no optical surface having a pre-defined optical center. However, careful measurement of the wearer's eyes can yield a determination of where the optical center of each lens should be placed in the frame. It is then possible, though not easy, to prepare a contoured pattern having a center hole located precisely where the optical center of the lens should be. This hole is then used as the bore through which the contoured pattern is mounted on the floating axle of the edge grinder. The precise location of this hole relative to the predetermined optical center is another step requiring great precision and which frequently leads to mistakes which are costly and time-consuming to correct.
Moreover, it should be recognized that most eyeglass frame sockets do not offer a flat or planar surface when laid against a pattern to be traced and cut. This further contributes to the likelihood of errors in the process.
The present inventors are aware of other edging systems in the prior art.
U.S. Pat. No. 765,268 shows a stencil 52 mounted on a shaft 51. A follower 24 contacts the stencil 52 and is mechanically coupled so that as the follower encounters higher or lower portions of the stencil, an etcher will mimic the same motion against a blank 59. However, it is especially useful to note that the mounting of both the stencil and the blank are on flat surfaces thereof, and not against an optically curved surface.
Not all edging machines are applied to lenses or even glass. U.S. Pat. No. 548,298 discloses a key duplicator in which an existing key is surfaced as a stencil, and is gripped on opposite sides. A follower floats against the ridges of the key and is mechanically coupled to an edger which inscribes substantially identical ridges in a key blank. Of course, this reference does not involve gripping optical surfaces.
U.S. Pat. No. 3,641,711 discloses a machine which is specifically designed for conforming edges of glass to a pre-determined form. However, the form is a track 33 rigidly mounted on posts 34. A follower contacts and moves about the edge of the template and carries an edge grinding tool around a glass blank to produce a corresponding shape. This machine does not contemplate random variations in a template to match non-standardized eyeglass frame requirements. It is apparently intended primarily for mass production of items such as decorative windows or table surfaces.
U.S. Pat. No. 2,356,448 discloses an apparatus in which a lens or similar article is supported on a curved surface. As seen in FIG. 3, the stencil 56 is supported at 57, and made to contact follower roller 63 which in turn drives edge grinding of a number of duplicate lens objects. However, the reference does not consider the stencil 56 to be readily removable, and does not specify the manner in which the support 57 grips the stencil 56. This implies that the stencil 56 is permanently mounted. This and the production of multiple duplicate lenses strongly suggest that the machine is a mass production device.
It therefore remains clear that there is a need and a demand for a reliable system of circumference tracing and duplication which avoids the various sources of error seen in the prior art. The system should accommodate rapid optical centering of the contoured pattern, as well as mounting of the pattern at its predetermined center to the floating axle of the grinding system. The improvement should require little or no change of the present edge grinders now universally utilized in the retail vision assistance industry.